Regenerative brake

ABSTRACT

A lightweight regenerative brake having a large braking force is provided. A regenerative brake  1  comprises a brake disc ( 10 ) and a pair of stators ( 20 ) to perform regenerative braking. This regenerative brake ( 1 ) reduces the heat generated in the brake disc ( 10 ), because a part of the kinetic energy of a railway car is regenerated by generation of electricity in a tertiary circuit of the power source side when the brake is applied, and consequently the amount of energy converted into heat energy is decreased. Compared to a conventional regenerative brake, this regenerative brake ( 1 ) enables the disc ( 10 ) to be made thinner and dispenses with a cooling device such as a fan. Accordingly, a small-sizes and lightweight brake having a large braking force can be constituted using this regenerative brake ( 1 ).

TECHNICAL FIELD OF THE INVENTION

This invention relates to a regenerative brake for a railway car.

BACKGROUND OF THE INVENTION

Conventionally, there has been an eddy current brake which performsbraking by electromagnetic induction using a three-phase alternatingcurrent, as described in the Unexamined Japanese Patent Publication No.61-266064. As shown in FIG. 6, such an eddy current brake 100 comprisesa brake disc 102 attached to an axle 106 so that a disc surface 104 isperpendicular to the axle 106, and a stator 108 which is provided in aposition facing the disc surface 104 and which, when excited, generatesa moving magnetic field which moves to a direction opposite to arotation direction of the brake disc 102. The eddy current brake 100moves the moving magnetic field so that the slip reaches one (1) ormore, as shown in FIG. 7. When this moving field excited by the stator108 generates an eddy current on the disc surface 104, a force operatingto a direction opposite to the rotation direction of the brake disc 102is applied to the brake disc 102 according to the Fleming's left-handrule, and thus, braking is performed using the force.

In the eddy current brake 100, almost all the kinetic energy of a wheel110 is converted into heat energy by the eddy current passing on thebrake disc 102, and consequently the brake disc 102 becomes hot.However, it is clearly not structurally preferable that a temperature ofthe brake disc 102 becomes high exceeding a certain temperature.Therefore, in the conventional eddy current brake 100, the brake disc102 is made thick to increase heat capacity and to facilitate heatradiation. Also, a cooling device such as a fan is provided to cool thebrake disc 102 forcibly so as to prevent the brake disc 102 from gettingtoo hot exceeding the certain temperature.

On the other hand, to speed up a railway car of a bullet train, etc., itis necessary to reduce the weight of the car and to enhance the brakingforce

However, the conventional eddy current brake 100 requires thicker brakedisc 102 to increase heat capacity, etc. and a fan to be provided toenhance the braking force, thereby resulting in increase in weight.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a regenerative brakefor performing braking by electromagnetic induction, which issmall-sized and lightweight in spite of the larger braking forcecompared to a conventional eddy current brake.

In order to attain the above object, the present invention provides aregenerative brake comprising a brake disc attached coaxially to an axleof a wheel of a railway car and a stator for braking provided in aposition facing a disc surface of the brake disc, wherein theregenerative brake brakes the brake disc by exciting coils provided onthe stator and generating a moving magnetic field which moves to thesame direction with a rotation direction of the brake disc at a lowerspeed than a rotation speed of the brake disc, and, along with thebraking, regenerates a part of the kinetic energy of a railway car inthe power source side via the stator.

In other words, the regenerative brake of the present invention, ifexplained with a graph showing a characteristic curve of a conductivedevice shown in FIG. 7, does not brake when the slip reaches one (1) ormore like the conventional eddy current brake but does brake when theslip is less than zero.

When braking is performed when the slip is less than zero as such, apart of the kinetic energy of the railway car is regenerated in thepower source side upon braking and the amount of energy converted intoheat energy is decreased compared with a case of the eddy current brakedescribed in the prior art, resulting in that less heat is generated inthe brake disc. Therefore, with the regenerative brake of the presentinvention, there is no need to increase heat capacity of the brake discas in the eddy current brake, and consequently it is possible to formthe brake disc thin and to dispense with a cooling device such as a fan.

Accordingly, the regenerative brake of the present invention can besmall-sized and lightweight even though the braking force is larger thanthat of the eddy current brake described in the prior art.

Additionally, it is preferable that the stator is formed as large as itcovers a part of the disc surface as in the regenerative brake of thepresent invention. Formed as such, a heat radiation effect of the brakedisc becomes significant and the brake disc can be constituted thinner.Also, no cooling device is required. As a result, the eddy current brakeof the present invention can be made small-sized and lightweight.

Particularly, it is preferable that the stator is formed into a sectorextending along the circumference of the brake disc and comprises astator core which is formed to have a plurality of coils provided alongthe arc of the sector. Such a stator allows the moving field to movealong the rotation direction of the brake disc and the braking force tooperate along the rotation direction of the brake disc. Therefore, it ispossible to apply the braking force to the brake disc efficiently.

As another example, it is preferable that the stator comprises anelongate stator core which is arranged so that the longitudinal lengthof the stator core is parallel to a traveling direction of the railwaycar. Such arrangement allows the longitudinal length of the stator coreand the traveling direction of the train to be parallel to each other,and consequently, the air passes on the brake disc efficiently.Accordingly, since the heat radiation effect is significant and thebrake disc can be made further thinner, the regenerative brake can bemade small-sized and lightweight

A power car to which a motor is attached, so-called M car, comprises aninductive motor and the inductive motor performs regenerative braking.Therefore, there is no need to attach the eddy current brake of thepresent invention. However, non-powered car, so-called T car, does notcomprise an inductive motor. Therefore, it is significantly important toperform regenerative braking with the eddy current brake of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective illustration of one end of a wheel to which aregenerative brake of the present embodiment is attached;

FIG. 2 is a cross sectional view of a brake disc;

FIG. 3 is a cross sectional view taken along the line A-A′ of FIG. 1;

FIG. 4 is a block diagram of an operation circuit;

FIG. 5 is a front elevation view of the brake disc for explaining theother example of a stator core;

FIG. 6 is a perspective view of a conventional eddy current brake; and

FIG. 7 is a graph showing a characteristic curve of an induction device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be described, by way of example, with referenceto the accompanying drawings.

FIG. 1 is a perspective view of one end of a wheel to which aregenerative brake of the present embodiment is attached, FIG. 2 is across sectional view of a brake disc, FIG. 3 is a cross sectional viewof a stator (cross sectional view taken along the line A-A′ of FIG. 1),FIG. 4 is a block diagram of an operation circuit, and FIG. 5 is a frontelevation view of the brake disc.

As shown in FIG. 1, a regenerative brake 1 of the present embodimentcomprises a brake disc 10 and a pair of stators 20 and 21.

The brake disc 10 is attached concentrically to an axle 9 provided on atruck of a railway car. The brake disc 10, as shown if FIG. 2 inparticular, is composed of a cylindrical portion 14 and a disc portion16. The disc portion 16 has a first surface 12 and a second surface 13.The cylindrical portion 14 is formed into a circular cylinder, and fixesthe brake disc 10 on the axle 9 with the cylindrical portion 14 beingfitted on the axle 9. On the other hand, the disc portion 16 is formedin a three-layer structure in which an iron disc 16 a is sandwichedbetween two aluminum discs 16 b, and is integrally attached to an outercircumferential surface of the cylindrical portion 14 to be concentricwith the cylindrical portion 14. The disc 16 a may be composed of anymagnetic body having strength such as steel besides iron. The disc 16 bmay be composed of any non-magnetic body having high conductivity.

The stators 20, 21 are arranged to face a disc surface 12 of the brakedisc 10 and to interpose the brake disc 10 above the axle 9. As stators20, 21 are similar to each other, only the first stator is shown indetail. The stator 20 is composed of a stator core 22 and a statorwinding 24, as shown in FIG. 3 in particular. The stator core 22 isformed to extend parallel to a traveling direction of the railway carand to the disc surface 12. On one side of the stator core 22 facing tothe disc surface 12, a plurality of slits 22 a formed perpendicular tothe longitudinal length of the stator core 22 are provided at evenintervals along the longitudinal length.

In order to generate a moving field, the stator winding 24 is composedof coils 24 a-24 c of three phases: U phase, V phase and W phase. Thecoils 24 a-24 c are aligned facing to the disk surface 12 of the brakedisc 10 along the traveling direction of the railway car so that awinding surface around which a conductive wire composing each of thecoils 24 a-24 c is wound is parallel to the disc surface 12 of the brakedisc 10. Each of the coils 24 a-24 c is formed into a concentrated aswell as short-pitch winding and is fit into the slits 22 a on the statorcore 22 to which the stator winding 24 of each of the phases is to beallocated. Each of the coils 24 a-24 c is attached to one of the statorcores 22 so that the coils 24 a-24 c of an equal phase face to eachother and so as not to cancel each other's magnetic flux. The presentembodiment shows the coils 24 a-24 c of a short-pitch winding arrangedat each coil pitch of three slots to a pole pitch of four slots, as anexample. However, other constitutions are also acceptable.

An operation circuit for operating the regenerative brake of the presentembodiment is now explained.

FIG. 4 is a block diagram of the operation circuit.

An operation circuit 30 of the present embodiment comprises a converter32, an inverter 34, a rotation speed sensor 36 and a control circuit 38,as shown in FIG. 4. The converter 32 converts electricity of a singlephase 440V of a tertiary winding into a direct current, for use in anauxiliary circuit among the main transformer windings which step down anextra high tension supplied from an overhead wire to be outputted to theinverter 34. The auxiliary circuit is a circuit which supplieselectricity to in-vehicle equipment such as an air conditioningapparatus and ventilator.

The inverter 34 converts the direct-current electricity supplied fromthe converter 32 into a three-phase alternating current by PWM controland outputs the same to the stator winding 24. The converter 32 and theinverter 34 are constituted using an IGBT (insulated gate bipolartransistor) element.

The rotation speed sensor 36 is attached to the brake disc 10 to measurea rotation speed of the brake disc 10, and outputs a speed signalindicating the rotation speed of the brake disc 10 to the controlcircuit 38. The rotation speed of the brake disc 10 is calculated in thecontrol circuit 38 based on the speed signal inputted from the rotationspeed sensor 36, and according to the calculated result, PWM (pulsewidth modulation) control is performed to operate the inverter 32. Inthe PWM control, the stator winding 24 is excited and a moving magneticfield is generated which moves at a speed lower than the rotation speedof the brake disc 10 calculated by the control circuit 38 to the samedirection as the rotation.

In the operation circuit 30, the tertiary circuit which consumes powersupplied from the stator winding 24 upon regenerative braking andconverted into a direct current in the inverter 34 may be insertedbetween the converter 32 and the inverter 34. Also in the operationcircuit 30, if the power of the auxiliary circuit has already been adirect current, the electricity may be supplied directly to the inverter32, and not via converter 32.

If the regenerative brake 1 constituted as the above is controlled usingthe operation circuit 30, it operates as follows.

When the regenerative brake 1 of the present embodiment started tobrake, an electric current is passed to the coils 24 a-24 c provided onthe stators 20 by PWM control. Then, a moving field is generated whichmoves at a speed lower than the rotation speed of the brake disc 10 tothe same direction as the rotation direction of the brake disc 10through the disc 16 b of the brake disc 10, and an eddy current isgenerated on the brake disc 10. As a result, a force is applied to adirection opposite to the rotation direction according to the Fleming'sleft-hand rule, and this force becomes a braking force to brake thebrake disc 10.

This braking is a regenerative braking and kinetic energy of the railwaycar is partly converted into electricity. The electricity is convertedinto a direct current in the inverter 34 which serves as a converter,and is outputted to the power source side. The kinetic energy is partlyconverted into heat energy to heat the brake disc 10.

The following effects are expected when the regenerative brake 1 asexplained above is used.

As above described, if braking is performed when the slip is less thanzero, a part of the kinetic energy of the railway car is regenerated inthe power source side upon braking and the amount of energy convertedinto heat energy is decreased compared to that in case of the eddycurrent brake described in the prior art, resulting in that less heat isgenerated in the brake disc. Therefore, there is no need to increaseheat capacity of the brake disc 10 with the regenerative brake of thepresent invention as in the eddy current brake, and consequently it ispossible to form the brake disc thin and to dispense with a coolingdevice such as a fan. Accordingly, the regenerative brake 1 of thepresent embodiment can be constituted small-sized and lightweightcompared to the eddy current brake described in the prior art even ifthe braking force is increased.

The regenerative brake 1 of the present embodiment is formed as large asit covers a part of the disc surface of the brake disc 10. Therefore, adramatic heat radiation effect can be achieved which allows productionof the thinner brake disc 10 and lack of a cooling device. As a result,the eddy current brake of the present embodiment can be constitutedsmall-sized and lightweight compared to the conventional eddy currentbrake.

In the present embodiment, the longitudinal length of the stator core 22and the traveling direction of the train is parallel to each other andthereby the air passes on the brake disc 10 efficiently. Accordingly,since a dramatic heat radiation effect can be achieved compared to theconventional eddy current brake and therefore the brake disc 10 can bemade further thinner, the regenerative brake 10 of the presentembodiment can be constituted smaller-sized and lighter-weight than theconventional eddy current brake.

The stator core 22 may be formed into a sector extending along thecircumference of the brake disc 10 and the coils 24 a-24 c may bearranged along the circumference of the sector as shown in FIG. 5. Inthis manner, the moving magnetic field moves along the rotationdirection of the brake disc 10 and the braking force operates along therotation direction of the brake disc 10. Then, the braking force can beapplied to the brake disc 10 efficiently.

It is not necessary to provide a power car to which a motor is attached,so-called M car, with the regenerative brake of the present embodiment,since the M car comprises an induction motor which performs regenerativebraking. However, there is a significant importance in providing anon-powered car, so-called T car, with the regenerative brake of thepresent embodiment and performing regenerative braking, since the T cardoes not comprise an induction motor.

It is known that a braking force of the conventional eddy current brakegets small if a rotation speed of a rotor, namely, the brake disc 10, isslow, and consequently, a control brake does not work when a speed of arailway car is equal to or under 70 km per hour.

It is then preferable as in the present embodiment that the moving speedof the moving magnetic field generated in the stator 20 may becontrolled so that, as shown in FIG. 7, the slip S to the rotation speedof the brake disc 10 corresponding to a rotor is, among a range α ofFIG. 7, within a range of values between the value at which the sametorque value (γ, point in FIG. 7) with the maximum torque value (β pointin FIG. 7) when the induction device is treated as a brake is obtainedand the value at which the maximum torque can be obtained, for example.

In this manner, it is possible to obtain an extremely high torque, thatis, braking force, in spite of the low rotation speed of the rotor.Further in this manner, despite the high braking force, braking requiresless primary current. Accordingly, generation of heat in the brake disc10 is reduced and the brake disc 10 can be thinner. As a result, theregenerative brake 1 of the present embodiment can be made lightweight.

The present invention should not be limited to the described embodiment,and other modifications and variations might be possible withoutdeparting from the scope of the invention.

For instance, the rotation speed sensor 26 measures the rotation speedof the brake disc 10 in the present embodiment. However, if in advance atable which shows relevancy between the train speed and the rotationspeed of the brake disc 10 is provided and calculation of the movingspeed of the moving magnetic field is possible as a result of measuringthe train speed, thus PWM control may be directly performed based on thetrain speed by removing the rotation speed sensor 26

In addition, the converter 32 and the inverter 34 are composed of anIGBT element in the present embodiment. However, they may be composed ofan electric semiconductor such as a GTO thyristor (gate turn-offthyristor), etc.

Moreover, although a short-pitch winding is described in the presentembodiment, other windings such as a distributed winding, etc may beutilized.

INDUSTRIAL AVAILABILITY

As described in details in the above, the regenerative brake of thepresent invention can be constituted small-sized and lightweight inspite of a large braking force compared with the conventional eddycurrent brake.

1. A regenerative brake comprising: a brake disc attached to an axle ofa railway car, comprising a first disc surface; a second disc surface; afirst stator comprising three or more first stator coils directlyopposing the first disc surface; a second stator comprising three ormore second stator coils directly opposing the second disc surface; arotation speed sensor for measuring a rotational speed of the brakedisc; an inverter; and a control circuit; wherein the regenerative brakeopposes rotation of the brake disc by exciting the three or more firststator coils and the three or more second stator coils across the brakedisc, thereby generating a moving magnetic field, the rotation speedsensor measures the rotational speed of the brake disc; the controlcircuit causes the generated moving magnetic field to move at a slowerspeed than the rotational speed of the brake disc; a portion of kineticenergy, resulting from motion of the railway car, is converted toelectricity by the first stator and the second stator; the electricitygenerated by the first and second stators is supplied to the inverter;the inverter converts the electricity into direct-current electricity;and the direct-current electricity is supplied to an electrical systemfor the railway car.
 2. The regenerative brake according to claim 1,wherein the first stator is formed so as to directly oppose one half ofthe first disc surface of the brake disc, and the second stator isformed so as to directly oppose one half of the second disc surface ofthe brake disc.
 3. The regenerative brake according to claim 2, whereinthe first stator is formed into a first sector extending along acircumference of the brake disc and comprises: a first stator core inwhich the three or more first coils are provided along an arc of thefirst sector, and the second stator is formed into a second sectorextending along a circumference of the brake disc and comprises; asecond stator core in which the three or more second coils are providedalong an arc of the second sector.
 4. The regenerative brake accordingto claim 2, wherein the first and second stators comprise respectiveelongate first and second stator cores which are arranged so that alongitudinal length of the respective first and second stator coresextend parallel to a tangent to a direction of movement of the railwaycar.
 5. The regenerative brake according to claim 1, wherein theregenerative brake is supplied for a non-powered railway car tofacilitate braking of the non-powered railway car.
 6. The regenerativebrake according to claim 1, wherein the brake disc further comprises: athree-layer structure in which a magnetic core is sandwiched between twoaluminum discs; and the control circuit controlling movement of themagnetic field along a circumference of the brake disc at a speed slowerthan the rotational speed of the brake disc and a speed of movement ofthe magnetic field being dependent upon the rotational speed of thebrake disc.
 7. The regenerator brake according to claim 6, wherein themagnetic core is iron.
 8. The regenerative brake according to claim 6,wherein the magnetic core is steel.
 9. The regenerative brake accordingto claim 1, wherein when a slip value of the regenerative brake reaches1, the regenerative brake fails to apply a braking force.
 10. Theregenerative brake according to claim 1, wherein when a slip value ofthe regenerative brake ranges from 0 to −1, the regenerative brakeapplies a braking force.
 11. A regenerative brake comprising: a brakedisc attached to an axle of a railway car, the brake disc having a firstand second opposed surfaces; a first stator having at least three firststator coils located adjacent the first disc surface; a second statorhaving at least three second stator coils located adjacent the seconddisc surface; a rotational speed sensor for measuring the rotationalspeed of the brake disc; a control circuit electrically coupled with therotational speed sensor; an inverter electrically coupled with the firstand second stators and the control circuit, the regenerative brakeretards rotation of the brake disc, during operation of the regenerativebrake, by exciting the at least three first stator coils and the atleast three second stator coils across the brake disc, therebygenerating a magnetic field, the control circuit generating the magneticfield and controlling movement of the magnetic field along acircumference of the brake disc at a speed slower than the rotationalspeed of the brake disc to generate a braking effect on the rotatingbrake disc with a speed of movement of the magnetic field beingdependent upon the rotational speed of the brake disc; and the firststator and the second stator converting kinetic energy of the railwaycar to electricity which is supplied to the inverter, the inverterconverts the electricity to a direct current electricity which issupplied to an electrical system of the railway car.
 12. Theregenerative brake according to claim 11, wherein the first stator isarcuate in shape and concentric with the first surface of the brake discand the first stator has a radius similar to a radius of the first discsurface, and the second stator is arcuate in shape and concentric withthe second surface of the brake disc and the second stator has a radiussimilar to a radius of the second disc surface.
 13. The regenerativebrake according to claim 12, wherein the first stator extendscircumferentially about the brake disc and has a first stator core inwhich the at least three first stator coils are provided along an arcthereof; and the second stator extends circumferentially about the brakedisc and has a second stator core in which the at least three secondstator coils are provided along an arc thereof.
 14. The regenerativebrake according to claim 12, wherein the first and second statorscomprise respectively elongate first and second stator cores which arearranged so that a longitudinal length of the respective first andsecond stator cores extend parallel to a tangent to a direction ofmovement of the railway car.
 15. The regenerative brake according toclaim 11, wherein the regenerative brake is provided on a non-poweredrailway car to facilitate braking of the non-powered railway car. 16.The regenerative brake according to claim 11, wherein the brake discfurther comprises a three-layer structure in which a central magneticcore layer is sandwiched between two aluminum disc layers.
 17. Theregenerator brake according to claim 16, wherein the central magneticcore layer comprises iron.
 18. The regenerative brake according to claim16, wherein the central magnetic core layer comprises steel.
 19. Theregenerative brake according to claim 11, wherein the regenerative brakedoes not apply a braking force when a slip value of the regenerativebrake is 1 or greater.
 20. The regenerative brake according to claim 11,wherein regenerative brake applies a braking force when a slip value ofthe regenerative brake is ranges from 0 to −1.